The present invention relates to an amplifier-type solid-state image sensor device for obtaining a signal charge using a photoconverter such as a photodiode, amplifying and extracting the obtained signal charge, and more particularly relates to an amplifier-type solid-state image sensor device wherein the positional relationship between the photoconverter and an opening in a metal film which defines the region where light is received in the photoconverter, is improved.
A solid-state image sensor device for obtaining an image of an object using a lens has a problem that pixels near the center of the semiconductor chip have a different amount of light injected thereto from pixels near the peripheral portion of the semiconductor chip. More specifically, the amount of light in the center of the semiconductor chip is great, but the amount of light at the peripheral portion of the semiconductor chip is small. Consequently, the level of photo-sensitivity differs between at the center of the semiconductor chip and the peripheral portion of the semiconductor chip. Conventionally, this problem is solved by a method known as scaling, whereby the position of a microlens in the color filter portion is slightly displaced horizontally toward the center of the photodiode (by approximately 0.001 xcexcm per pixel). Scaling prevents the level of photosensitivity at the peripheral portion of the semiconductor chip from falling below that at the center the semiconductor chip.
In a CCD-type solid-state image sensor device, as shown in FIG. 6, an aluminum lightproof film (or aluminum wire) 65, which defines the opening in the photodiode 62, covers capacitor electrodes (polysilicon) or gate wires (polysilicon) 63 and extends to the edge of the photodiode 62. Therefore, the difference in level between the surface of the photodiode 62 and the lightproof film 65 in the opening, is almost entirely dependent on the thickness of the lightproof film 65. Since the lightproof film 65 is extremely thin, the difference in level between the surface of the photodiode 62 and the lightproof film 65, which defines the opening, is extremely small. This makes it possible to correct photosensitivity using the scaling method described above. In FIG. 6, the numeral 61 represents a semiconductor substrate, 64 represents an interlayer insulating film, 66 and 67 represents flattening insulating films, and 68 represents a microlens.
By contrast, in an amplifier-type solid-state image sensor device known as a CMOS sensor, the difference in level between the surface of the photodiode 72 and the metal film (aluminum wire, or aluminum lightproof film, or the like) 74, which defines the opening, is generally more than 1 xcexcm, as shown in FIG. 7. As a result, even when the conventional technique of scaling is carried out using the microlens 76 of the color filter portion, the metal film 74, which defines the opening of the photodiode 72, cuts off the injected light, reducing the amount of light injected to the photodiode 72 at the peripheral portion of the semiconductor chip. Therefore, sensitivity cannot be adequately corrected by scaling with the microlens 76. Thus conventional CMOS sensors have a disadvantage that sensitivity cannot be adequately corrected, due to the fact that the difference in level between the surface of the photodiode and the metal film which defines the opening, is more than 1 xcexcm, thereby making it impossible to match the amount of light injected at the center of the semiconductor chip to the amount injected at the peripheral portion of the semiconductor chip, even by scaling with the microlens. In FIG. 7, numerals 73 and 74 represent insulating films for flattening, 77 represents an object lens, and 78 represents the light path.
The present invention has been devised to solve the problems described above, and aims to provide an amplifier-type solid-state image sensor device wherein the amounts of light injected to the center and peripheral portion of the image sensing region can be matched even when there is a considerable difference in level between the surface of the photodiode and the metal film which defines the opening, thereby obtaining closely similar levels of photosensitivity at the center and peripheral portion of the image sensing region.
In order to solve the problems described above, an amplifier-type solid-state image sensor device according to a first aspect of the present invention comprises a plurality of unit cells, each comprising a photoconverter and a signal scanning circuit, arranged two-dimensionally in an image sensing region on a semiconductor substrate; signal lines provided on the semiconductor substrate, for reading out signals from the cells in the image sensing region; and a metal film having openings defining regions of the photoconverters of the unit cells, onto which regions light is radiated through the openings, a center position of each of the openings of the metal film being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the amplifier-type solid-state image sensor device may further comprise microlenses arranged for the unit cells, a center position of each of the microlenses being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the metal film may comprise a aluminum wire film.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the metal film may comprise a film made of a refractory metal.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the refractory metal may include titanium, tungsten, and molybdenum.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the metal film may comprise a film made of a metal compound.
In the amplifier-type solid-state image sensor device according to the first aspect of the present invention, the metal film may comprise a aluminum lightproof film.
An amplifier-type solid-state image sensor device according to a second aspect of the present invention comprises a plurality of unit cells, each comprising a photoconverter and a signal scanning circuit, arranged two-dimensionally in an image sensing region on a semiconductor substrate; signal lines provided on the semiconductor substrate, for reading out signals from the cells in the image sensing region; and a metal film having openings defining regions of the photoconverters of the unit cells, onto which regions light is radiated through the openings, a center position of each of the openings of the metal film being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell, the areas of those of the openings of the metal film, which are in a peripheral portion of the image sensing region, being larger than the areas of those of the openings of the metal film, which are in a center portion of the image sensing region.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the amplifier-type solid-state image sensor device may further comprise microlenses arranged for the unit cells, a center position of each of the microlenses being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the metal film may comprise a aluminum wire film.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the metal film may comprise a film made of a refractory metal.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the refractory metal may include titanium, tungsten, and molybdenum.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the metal film may comprise a film made of a metal compound.
In the amplifier-type solid-state image sensor device according to the second aspect of the present invention, the metal film may comprise a aluminum lightproof film.
An amplifier-type solid-state image sensor device according to a third aspect of the present invention comprises a plurality of unit cells, each comprising a photoconverter and a signal scanning circuit, arranged two-dimensionally in an image sensing region on a semiconductor substrate; signal lines provided on the semiconductor substrate, for reading out signals from the cells in the image sensing region; and a metal film having openings defining regions of the photoconverters of the unit cells, onto which regions light is radiated through the openings, a center position of each of the openings of the metal film being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell, the areas of those of the openings of the metal film, which are in a peripheral portion of the image sensing region, being larger than the areas of those of the openings of the metal film, which are in a center portion of the image sensing region, the areas of the photoconverters of those of the unit cells, which are in a peripheral portion of the image sensing region, being larger than the areas of the photoconverters of those of the unit cells, which are in a center portion of the image sensing region.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the amplifier-type solid-state image sensor device may further comprise microlenses arranged for the unit cells, a center position of each of the microlenses being displaced to the side of the center of the image sensing region with respect to a center position of the photoconverter of a corresponding unit cell.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the metal film may comprise a aluminum wire film.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the metal film may comprise a film made of a refractory metal.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the refractory metal may include titanium, tungsten, and molybdenum.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the metal film may comprise a film made of a metal compound.
In the amplifier-type solid-state image sensor device according to the third aspect of the present invention, the metal film may comprise a aluminum lightproof film.
The effects of the present invention are as follows. By displacing the center of the opening region of the metal film to the sides of the center of the image sensing region with respect to the center of the photoconverter, it is possible to prevent light diagonally entering the photoconverter from being cut off by the metal film, consequently avoiding reduction of sensitivity in the peripheral portions of the image sensing region. Therefore, even when there is a considerable difference in level between the surface of the photodiode and the metal film defining the openings, the amounts of light entering the center and peripheral portions of the image sensing region can be matched, thereby obtaining similar sensitivity in the center and peripheral portions of the image sensing region.
Furthermore, since the opening regions of the metal film near the peripheral portion of the image sensing region are wider than the opening regions of the metal film near the center of the image sensing region, reduction in sensitivity in the peripheral portion of the image sensing region can be reduced even more reliably.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.